FIG. 6 is a diagram schematically illustrating the structure of a stage device according to an example of the prior art. This diagram exemplifies the structure of a reticle stage for positioning a reticle when a semiconductor is manufactured (for example, see the specification of Japanese Patent Application Laid-Open No. 2000-77503).
The reticle stage shown in FIG. 6 is disposed on a plumb upper surface serving as a reference surface on a stage base 101. The stage base 101 is arranged to oppose a guide 102 via bearings 103 and is guided in a traveling direction X and in a direction Y (a yaw direction) at right angles to the direction X. Ball bearings or slide bearings are used as the bearings 103, though static-pressure bearings, or the like, may be used if attitude is to be maintained with a high degree of precision.
Movable magnets 107 are disposed on both sides of a slider 104 in terms of the horizontal direction. When a current is passed into motor coils 108 opposing the movable magnets 107, the slider 104 is driven in the traveling direction. Since there are many cases wherein the slider is driven at a high acceleration in a reticle stage, or the like, often the side of the motor coil 108 is arranged as a countermass 106. The countermass 106 also is placed on the stage base 101 via the bearings 103 in similar fashion and is driven on the stage base in the direction opposite to that of the slider 104 thereby to counter or to cancel the reaction force so that oscillation externally of the stage device can be suppressed.
In the case of a semiconductor exposure apparatus that employs light (e.g., I rays, a KrF excimer laser, etc.) as a light source 109, a transmission-type reticle 105 is mounted on the slider 104 and is illuminated with light from above, whereby a circuit pattern on the reticle 105 is transferred to a wafer.
An exposure apparatus that uses EUV (extreme ultraviolet) light as the light source has become the focus of attention in recent years as a next-generation exposure apparatus. In the case of exposure using EUV light, consideration has been given to an arrangement in which a reflecting-type reticle is mounted on the plumb lower surface of the slider 104, as illustrated in FIG. 7.
With the above-mentioned exposure apparatus that uses EUV light, the reticle 105 is disposed on the lower surface of the slider 104. Consequently, in order to illuminate the reflective surface of the reticle 105 with EUV light that impinges obliquely with respect to the horizontal direction, it is necessary that the stage base 101 be provided with an opening through which the light can pass.
In the arrangement of FIG. 7, however, the optical path and the stage base 101 interfere. In order to avoid such interference, therefore, it is required that the countermass 106 be disposed farther toward the outer side. This leads to an increase in the size of the stage device.
Further, with the arrangement in which the stage base 101 is provided with the opening, there is the danger that the stage base 101 will be deformed owing to inadequate rigidity. If the stage base 101 is deformed owing to driving of the slider 104 at a high acceleration, the guide surface will be deformed. As a result, the attitude of the stage cannot be maintained and it will become difficult to achieve highly accurate positioning.